The invention relates to a dental implant comprising an anchoring part for anchoring within the bone and comprising a mounting part for receiving an element to be attached, such as an abutment or a crown, a bridge or a prosthesis construction.
Dental implants have been successfully used since more than 10 years. The major part of the dental implants currently used consist of titanium, since titanium has a sufficiently low elastic modulus and also has a relatively large strength. In addition, it is of particular importance that when using titanium as an implant material a safe integrating or interlocking osteogenesis can be reached when the surface is suitably treated (e.g. roughened by sand blasting). This means that the titanium implants, after reaching a primary stability by screwing into the bone, safely ossify within a healing time of about 3 to 4 months so that a permanent bond between the anchoring part screwed into the bone and the bone is guaranteed. Herein usually two-part implants are utilized. Basically, there are two possibilities for this end:
According to a closed sub gingival system the anchoring part of the implant is embedded until the bone ridge so that the mucoperiost cover can be sewn above the implant. Herein a drawback is the necessary secondary operation at the end of the primary healing phase for allowing a subsequent application of a mounting part, and thereon the desired prosthesis or crown.
By contrast, when using the open transgingival system, then the anchoring part of the implant can be sunk in up to about 3 mm above the bone ridge at mucosal level, thus avoiding a secondary operation. The wound edges can be directly adapted to the implant neck portion, thereby effecting a primary soft tissue closure to the implant.
Such a two-part implant construction for an open transgingival system is e.g. marketed by Institut-Straumann AG, Waldenburg/Switzerland under the mark ITI®DENTAL IMPLANT SYSTEM. Both the anchoring or primary part which is implanted transgingivally, as well as the assigned construction parts herein consist of pure titanium. To guarantee a good ossification the titanium surface is either coarsely sand blasted or is coated with titanium by thermal spraying. Both surfaces guarantee a good ossification or interlocking osteogenesis.
Thereafter onto the mounting part of such implants prosthesis elements, such as bridges or crowns, are usually screwed or cemented usually using intermediate so called abutments. Lately to this end also ceramic abutments have been developed that are applied onto the mounting part.
Ceramic abutments offer particular advantages during the subsequent matching of the supra-construction, such as bridges or crowns, to the abutment. They can be simply ground and allow to build constructions using prior art processes known to the dentist. Ceramic abutments offer particular advantages due to the fact that their color can be closely matched to the natural tooth color. Lately also abutments of zirconia have been developed which offer a particularly high strength.
Such a system consisting of two-part implants having an anchoring part and a mounting part, an abutment and a prosthesis applied thereon offers a good matching to the geometric situation for different indications, however, generally the multitude of the components used. is detrimental for the mechanical stability of the total system. Also each further bonding leads to possible starting points for bacteria which may cause parodontitis or gingivitis within the gap.
However, from an aesthetic point of view in particular in the front visible region it would be desired to make all transgingival parts, also the anchoring part, of ceramic. However, a screw connection between metal (anchoring part of titanium) and ceramic (mounting part) cannot be realized, inter alia, due to the differences in the coefficients of thermal expansion. By contrast, up to now anchoring parts made of ceramic could not pervade, since these usually do not have the necessary mechanical stability or do not provide safe ossification.
Lately also zirconia.ceramics have become available that have an extremely high strength, in particular when the shaped bodies are prepared by hot isostatic pressing or by sintering followed by hot isostatic densifying. Such a zirconia ceramic which may comprise roughly 92.1-93.5 wt.-% ZrO2, 4.5-5.5 wt.-% Y2O3 and 3.8-2.2 wt.-% HfO2, is for instance known from U.S. Pat. No. 6,165,925.
However, the application of zirconia ceramic as a material for making the anchoring part of an implant seems not possible, since a sufficient mechanical stability of the zirconia ceramic is necessary, this requiring a highly dense preparation, practically without any porosity to be measured, this simultaneously leading to a clean cut extremely hard surface.
Such a material is bio-inert, so that no interlocking osteogenesis is to be expected, this is why this material is not regarded to be suitable for the preparation of an anchoring part of an implant.
From DE 195 30 981 A1 a pre-manufactured fully ceramic implant supra-construction of zirconia is known for the design of artificial crown frustums of tooth color attached to implants. Although herein some kind of advantages with respect to the aesthetic of zirconia ceramic and possibly with respect to a simplified preparation for the design of the supraconstruction is made possible, however also this implant construction bears the basic disadvantages that rest with multiple-part implant constructions. Namely, since the implant itself consists of titanium, the same problems as before result within the bonding region between the implant and the supraconstruction made of zirconia ceramic.
Further reference is made to DE 40 12 731 A1 which discloses several processes for the treatment of implants to generate a defined coarse surface. However, the known system still suffers from the drawbacks inherent with metal implants.
Finally, reference is made to DE 28 38 759 A1 which discloses an implant consisting of a metal, a plastic or a ceramic that is covered with a layer system consisting of a passivating layer and/or of several physiologically active layers. Herein in particular a passivating layer of silicon nitride and a physiologically active layer of calcium fluoride, of carbon or the like is contemplated. However, also this implant does not guarantee a safe ossification within the bone after implantation.